MicroBiology MCQs with Answer and Explnation | Chapter 38

Answer: IgM

During the initial stages of an immune response, IgM antibodies are the first to be produced and reach the site of infection. IgM is particularly effective in agglutinating (clumping together) pathogens and activating the complement system. While IgM provides an early defense, other antibody classes, such as IgG, may become more prominent in the later stages of the immune response.

The other options are incorrect:

• IgA: IgA is found primarily in mucosal secretions like saliva and tears and plays a role in preventing infections at these surfaces. While it can contribute to immunity later in an infection, it’s not the first antibody to reach the site.
• IgE: IgE is primarily involved in allergic reactions and parasitic worm infections. It doesn’t play a significant role in early responses to most infections.
• IgG: IgG is the most abundant antibody in the blood and is the main antibody responsible for long-term immunity. However, it takes several days to be produced after initial exposure to a new antigen, making it slower than IgM in reaching the infection site.

Answer: The thymus gland

The thymus gland is the specialized organ responsible for T-cell development and selection. Here, T-lymphocytes undergo a rigorous selection process to ensure they can recognize and attack foreign invaders (pathogens) while avoiding attacking the body’s own tissues (self-tolerance). Only T-cells that pass this selection process mature into fully competent but not activated T-cells and leave the thymus to circulate in the blood and lymphatic system.

The other options are incorrect:

• The lymph nodes: Lymph nodes are secondary lymphoid organs that provide a platform for immune cells to interact with antigens and initiate an immune response. While T-cells can become activated in lymph nodes, they don’t develop there.
• The thyroid gland: The thyroid gland produces hormones that regulate metabolism. It has no role in immune cell development.
• The bone marrow: The bone marrow is the primary site of production for many blood cells, including B-lymphocytes (the precursors of antibody-producing plasma cells). However, T-lymphocytes only reside in the bone marrow temporarily before migrating to the thymus for development.

Answer: Galactose

A monosaccharide is a simple sugar consisting of a single sugar molecule. Galactose is one such example, containing six carbon atoms and an aldehyde group, making it a hexose monosaccharide.

The other options are incorrect:

• Sucrose: Sucrose is a disaccharide, meaning it is formed by the covalent linking of two monosaccharides (glucose and fructose) through a glycosidic bond. It is not a single sugar molecule.
• Lactose: Lactose is another disaccharide composed of glucose and galactose combined through a glycosidic bond.
• Maltose: Similar to lactose, maltose is a disaccharide consisting of two glucose molecules joined by a glycosidic bond.

Answer: Participates in feedback regulation

Allosteric inhibitors contribute to feedback regulation, a mechanism where the product of a metabolic pathway acts as an inhibitor for an earlier enzyme in the same pathway. By binding to an allosteric site (different from the active site), the inhibitor induces a conformational change in the enzyme, reducing its activity and consequently slowing down the production of its own product. This helps maintain homeostasis by preventing excess product accumulation.

The other options are incorrect:

• Causes the enzyme to work faster: While some allosteric molecules can act as activators and increase enzyme activity, inhibitors specifically decrease it.
• Binds to the active site: Allosteric inhibitors bind to a separate regulatory site, distinct from the active site where the substrate binds.
• Denatures the enzyme: Denaturation irreversibly unfolds the protein structure, completely inactivating the enzyme. Allosteric inhibition is a reversible process where the inhibitor can dissociate from the enzyme, restoring its activity.

Answer: a base + a sugar

A nucleoside is a molecule composed of two components. a nitrogenous base and a pentose sugar (ribose or deoxyribose). It lacks the third component, a phosphate group, which differentiates it from a nucleotide. Nucleosides form the building blocks of RNA and DNA, with nucleotides being the complete units linked together in these chains.

The other options are incorrect:

• a sugar + a phosphate: While phosphate is present in nucleotides, it’s not part of a nucleoside.
• a base + a phosphate: Similar to the previous option, this combination represents a phosphate group attached to a base, which is not a nucleoside.
• a base + a sugar + phosphate: This describes a nucleotide, which incorporates all three components: base, sugar, and phosphate.

Answer: Maltose

A disaccharide is a sugar molecule formed by the covalent linkage of two monosaccharides (simple sugars) through a glycosidic bond. Maltose is an example of a disaccharide, specifically consisting of two glucose molecules joined together.

The other options are incorrect:

• Glucose: Glucose is a monosaccharide, meaning it is a single sugar molecule and not formed by the joining of two simpler sugars.
• Fructose: Similar to glucose, fructose is another example of a monosaccharide.
• Galactose: While galactose can be part of disaccharides like lactose, it itself is a monosaccharide.

Answer: Glucose and galactose

Lactose is a disaccharide composed of two monosaccharide units, specifically glucose and galactose. They are bonded together through a glycosidic linkage.

The other options are incorrect:

• Glucose and fructose: While both are monosaccharides, lactose does not contain fructose.
• Glucose and sucrose: Sucrose is another disaccharide, but it is formed from glucose and fructose, not galactose.
• Glucose and ribose: Ribose is also a monosaccharide, but it is a pentose sugar with five carbon atoms, unlike the six-carbon hexoses like glucose and galactose found in lactose.

Answer: Dextran

Dextran is a bacterial and yeast polysaccharide, meaning it is a complex sugar molecule produced by both bacteria and yeast. It is formed by the polymerization of glucose molecules, typically with alpha (1-6) glycosidic linkages, though the specific branching pattern can vary depending on the source. Dextran has various applications in food, medicine, and industry due to its properties like water solubility, viscosity, and non-ionic nature.

The other options are incorrect:

• Starch: Starch is a plant polysaccharide primarily composed of amylose and amylopectin, both made up of glucose units linked with alpha (1-4) and alpha (1-6) glycosidic bonds, respectively. It is a major storage carbohydrate in plants and not produced by bacteria or yeast.
• Glycogen: Glycogen is another polysaccharide of glucose, but it is the primary storage carbohydrate in animals and fungi, not bacteria or yeast. Its structure is more highly branched than starch, with additional alpha (1-2) linkages between glucose units.
• Cellulose: Cellulose is the main component of plant cell walls and is a linear polysaccharide of glucose units linked with beta (1-4) glycosidic bonds, which gives it its strong and rigid structure. While some bacteria can degrade cellulose, they do not produce it themselves.

Answer: Homoglycan

A homoglycan is a polysaccharide where all the monosaccharide units are of the same type. So, if every sugar molecule in the chain is identical, you’re dealing with a homoglycan.

The other options are incorrect:

• Glycogen: While glycogen is a polysaccharide, it’s a heteroglycan. It consists of glucose units linked in a branched network, but with both alpha (1-4) and alpha (1-6) glycosidic bonds.
• Heteroglycan: As the name implies, a heteroglycan has different types of monosaccharide units linked together. For example, hemicellulose is a heteroglycan containing glucose, xylose, and other sugars.
• Oligosaccharide: An oligosaccharide is a short chain of sugar molecules, typically containing 3 to 10 monosaccharides. While they can be homo- or heteroglycans, the key differentiator is their shorter chain length compared to polysaccharides.

Answer: Glycogen

Among the options, only glycogen is a storage polysaccharide. It acts as the main energy reserve for animals and fungi, similar to how starch serves as the energy reserve for plants. Glycogen is primarily stored in muscles and the liver, readily accessible for quick energy release when needed.

The other options are incorrect:

• Cellulose: Cellulose is a structural polysaccharide, the primary component of plant cell walls. It provides rigidity and support to the plant structure but is not readily used for energy storage.
• Chitin: Similar to cellulose, chitin is a structural polysaccharide found in the exoskeletons of insects and crustaceans. It provides strength and protection but is not a storage molecule.
• Glucose: Glucose is a monosaccharide, the simplest form of sugar and the building block of various carbohydrates, including glycogen. However, it is not a storage molecule itself and is readily used for energy production in cells.

Answer: IgG

IgG is the champion of immunoglobulins, accounting for 70-75% of all antibodies found in the blood. This makes it the most abundant type by a significant margin. IgG plays a crucial role in long-term immunity, neutralizing toxins and viruses, and activating immune cells to eliminate pathogens.

The other options are incorrect:

• IgA: While IgA is the second most abundant immunoglobulin (around 10-15%), it’s mainly found in mucosal secretions like saliva, tears, and breast milk, protecting surfaces from infections.
• IgE: This immunoglobulin type makes up a mere 0.001% of the total and is primarily involved in allergic reactions and parasitic worm infections.
• IgM: IgM constitutes about 10% of immunoglobulins and is the first antibody produced in response to a new infection. However, its production declines once IgG takes over for long-term defense.

Answer: Starch

While glucose is the primary product of photosynthesis and a key energy source for plants, it’s too reactive and water-soluble for long-term storage. Instead, plants convert excess glucose into starch, a complex carbohydrate molecule made of linked glucose units. Starch forms dense, insoluble granules within plant cells, providing a stable and readily accessible energy reserve.

The other options are incorrect:

• Glycogen: This polysaccharide serves as the primary glucose storage molecule in animals but is not typically abundant in plants.
• Dextrin: Dextrin is a smaller polysaccharide than starch derived from its partial breakdown. It can be present in plants but not as the primary storage form of glucose.
• Cellulose: Cellulose is the main component of plant cell walls and provides structural support, not energy storage. It’s also a complex carbohydrate but with a different structure and function compared to starch.

Answer: Glycogen

The liver plays a crucial role in regulating blood sugar levels. When blood sugar rises after a meal, the liver absorbs excess glucose and converts it into a branched polysaccharide called glycogen for storage. This readily accessible glycogen reserve allows the liver to release glucose back into the bloodstream when needed, maintaining stable energy levels.

The other options are incorrect:

• Starch: While starch is the primary glucose storage molecule in plants, it’s not used for this purpose in animals. The liver only deals with glucose and its derivatives, not plant-specific compounds like starch.
• Dextrin: Dextrins are smaller glucose chains formed from the breakdown of starch and glycogen. They can be present in the liver but don’t serve as the main storage form of glucose.
• Cellulose: Similar to starch, cellulose is a plant-specific polysaccharide with a structural role unrelated to glucose storage in animal cells like those in the liver.

Answer: Chitin

Structural polysaccharides provide strength and support to biological structures. Among the listed options, only chitin functions in this way. It’s a major component of the exoskeletons of insects and crustaceans, cell walls of fungi, and some hard structures in other invertebrates. Chitin’s rigid, insoluble nature makes it ideal for providing structural stability.

The other options are incorrect:

• Glycogen Glycogen is a storage polysaccharide found in animals, particularly in the liver and muscles, and is not a structural polysaccharide.
• Starch: Starch is a storage polysaccharide found in plants and is not a structural polysaccharide.
• Glucose: This is a monosaccharide, the basic unit of carbohydrates, and doesn’t form the complex structures needed for structural roles.

Answer: Glycogen

Glycogen is analogous to starch. Both glycogen and starch are polysaccharides composed of glucose units linked together. They serve as storage forms of energy in living organisms. Glycogen is the main storage polysaccharide in animals, including humans, while starch is the primary storage polysaccharide in plants.

The other options are incorrect:

• Cellulose: While a complex carbohydrate like starch, cellulose serves a structural role in plant cell walls, not energy storage.
• Sucrose: This is a disaccharide, a simple sugar formed from two glucose molecules. While important for energy, it’s not a complex storage polysaccharide like starch or glycogen.
• Chitin: This polysaccharide serves primarily for structural purposes in the exoskeletons of insects and other invertebrates, not as an energy reserve.

Answer: Adenine

Purines are a type of nitrogenous base that forms part of the building blocks of nucleic acids like DNA and RNA. Of the listed options, only adenine (A) is a purine. The other three are pyrimidines, another type of nitrogenous base.

The other options are incorrect:

• Cytosine (C): Cytosine is a pyrimidine and pairs with guanine (G), another purine, in both DNA and RNA.
• Thymine (T): Thymine is a pyrimidine that only exists in DNA and pairs with adenine.
• Uracil (U): Uracil is a pyrimidine that replaces thymine in RNA and also pairs with adenine.

Answer: Thymine

Thymine is not a component of RNA. While it appears in DNA structure and pairs with adenine, RNA relies on a different pyrimidine base called uracil (U) to pair with adenine (A).

The other options are incorrect:

• Adenine (A): This is a major purine base present in both DNA and RNA, crucial for base pairing and information storage.
• Guanine (G): Another purine base found in both DNA and RNA, pairing with cytosine (C) for structural stability.
• Cytosine (C): This pyrimidine base occurs in both DNA and RNA, pairing with guanine to maintain double-stranded structure.

Answer: a base + a sugar + phosphate

A nucleotide is the fundamental building block of nucleic acids like DNA and RNA. It consists of three key components:

• A nitrogenous base: This can be either a purine (e.g., adenine, guanine) or a pyrimidine (e.g., cytosine, thymine in DNA, uracil in RNA). These bases provide the information-carrying capacity of DNA and RNA.
• A sugar molecule: This is either ribose in RNA or deoxyribose in DNA. The sugar gives the nucleotide its unique structure and provides a connection point for phosphate groups.
• A phosphate group: This provides a negative charge and is crucial for energy transfer and linking nucleotides together to form nucleic acid chains.

The other options are incorrect:

• a sugar + a phosphate: This is missing the critical component of a base, which defines the information content of the nucleotide.
• a base + a sugar: This is missing the phosphate group, which is necessary for energy transfer and linking nucleotides together
• a base + a phosphate: This combination is not a complete nucleotide because it lacks the sugar component.

Answer: Phosphodiester bond

A phosphodiester bond is the type of covalent bond that links adjacent nucleotides in a nucleic acid molecule like DNA or RNA. It forms between the phosphate group of one nucleotide and the sugar molecule (deoxyribose in DNA, ribose in RNA) of the next nucleotide. These strong bonds create the backbone of the nucleic acid chain, allowing it to store and transmit genetic information.

The other options are incorrect:

• Peptide bond: This type of covalent bond joins amino acids to form proteins, not nucleotides.
• Ionic bond: This is an electrostatic attraction between oppositely charged ions, not the type of bond that connects nucleotides.
• Covalent bond: While technically, a phosphodiester bond is a type of covalent bond, it’s a specific term used to describe the bonds between nucleotides in nucleic acids.

Answer: Pentose

The sugar molecule in a nucleotide is a pentose. In the context of DNA, the pentose sugar is deoxyribose, while in RNA, it is ribose. The term “pentose” refers to the fact that these sugars have five carbon atoms.

The other options are incorrect:

• Hexose: These sugars have six carbon atoms, one more than the pentoses needed in nucleotides. Examples include glucose and fructose.
• Tetrose: These sugars have four carbon atoms, one less than the pentoses needed in nucleotides.
• Triose: These sugars have three carbon atoms, two less than the pentoses needed in nucleotides.

Answer: Nucleotides

Nucleic acids, like DNA and RNA, are the fundamental building blocks of genetic material and play a crucial role in storing and transmitting hereditary information. These complex molecules are made up of smaller units called nucleotides.

The other options are incorrect:

• Nucleosides: While related to nucleotides, nucleosides are smaller units consisting of a sugar molecule and a nitrogenous base, lacking the phosphate group. They are precursors to nucleotides but not the actual building blocks of nucleic acids.
• Amino acids: These are the building blocks of proteins, another essential biomolecule, but not of nucleic acids. Amino acids have different chemical structures and functions compared to nucleotides.
• Histones: These are proteins that package and organize DNA within the nucleus of cells. They do not directly form the structure of nucleic acids but help compact and protect them.

Answer: Two

Adenine (A) and thymine (T) are complementary base pairs in DNA. They form two hydrogen bonds between their specific functional groups, contributing to the stability of the double-stranded DNA structure.

The other options are incorrect:

• One: While possible to envision a single hydrogen bond in some theoretical alignments, the standard and stable configuration involves two hydrogen bonds between adenine and thymine.
• Three: This number of hydrogen bonds is characteristic of the guanine (G) and cytosine (C) base pair, another important pair in DNA structure.
• Four: Four hydrogen bonds would be an unusually high number for a base pair and wouldn’t be energetically favourable for adenine and thymine.

Answer: Three

Guanine (G) and cytosine (C) form a complementary base pair in both DNA and RNA. Their specific functional groups allow them to form three hydrogen bonds with each other, contributing to the stability of the double-stranded structure.

The other options are incorrect:

• One: This wouldn’t be enough to provide sufficient stability for the base pair.
• Two: While two hydrogen bonds are present in the adenine-thymine pair, guanine and cytosine have the potential for three due to their specific chemical structures.
• Four: This would be an unnecessarily high number of hydrogen bonds and wouldn’t likely occur in the standard configuration of the G-C pair.

Answer: X-Ray crystallography

The arrangement of nucleotides in DNA can be visualized through X-Ray crystallography. This technique involves crystallizing a sample of DNA and exposing it to X-rays. The X-rays diffract off the crystalline structure, and the resulting diffraction pattern is used to determine the three-dimensional arrangement of atoms in the DNA molecule. X-ray crystallography played a crucial role in the discovery of the double helical structure of DNA by James Watson and Francis Crick.

The other options are incorrect:

• Ultracentrifuge: This instrument spins samples at high speeds to separate molecules based on their size and density. While useful for studying general properties of DNA, it can’t provide the detailed information about the arrangement of nucleotides that X-ray crystallography offers.
• Light microscope: This type of microscope uses visible light to magnify objects. However, the resolution of light microscopes is insufficient to directly visualize the individual atoms and their arrangement within a DNA molecule.
• Electron microscope: Electron microscopes use beams of electrons instead of light to achieve higher resolution. While they can be used to image the overall structure of DNA molecules, they are not commonly used to determine the specific order of nucleotides, as X-ray crystallography provides more detailed and accurate information.

Answer: Acute infection

A rise in anti-HBc immunoglobulin marks the body’s immune response to the Hepatitis B virus (HBV) core antigen. This rise typically occurs early in an acute HBV infection, between 2-6 weeks after exposure. Other markers for acute infection, like HBsAg, may not yet be detectable at this stage.

The other options are incorrect:

• Carrier state: While anti-HBc can also be present in carriers, it usually remains stable or declines over time. A sudden rise suggests ongoing, potentially active infection.
• Prodromal phase: The prodromal phase precedes the rise in anti-HBc and typically presents with vague symptoms like fatigue or nausea.
• Convalescence: During convalescence, anti-HBc levels usually decline as the infection resolves. An upward trend during this stage points towards potential progression or reactivation.

Answer: Virus

Cytopathic effect (CPE) refers to the visible changes or damage in infected cells caused by a virus. These changes can include cell rounding, lysis (bursting), inclusion bodies (viral protein aggregations), and syncytia (fusion of infected cells). Bacteria, spirochetes, and anaerobes generally do not induce these characteristic cellular changes.

The other options are incorrect:

• Bacteria: While bacteria can damage cells through toxins and other mechanisms, they typically don’t induce the specific morphological changes associated with CPE.
• Spirochete: Similar to bacteria, spirochetes primarily damage cells through physical disruption or toxin release, not by inducing distinct CPE features.
• Anaerobe: Being an anaerobe doesn’t directly relate to a microorganism’s ability to cause CPE. Some viruses require certain oxygen levels for replication, but the presence or absence of oxygen doesn’t determine the ability to induce CPE.

Answer: Fall in to the general size range of 200-3000 angstrom unit

This option accurately depicts one of the defining characteristics of viruses. Viruses are incredibly small, ranging from roughly 200 – 300 nanometers (nm) in diameter, which translates to 200-3000 angstroms. This size range significantly differentiates them from bacteria, which are considerably larger.

The other options are incorrect:

• New virus particle arises directly (by division) from preexisting viruses: While some viruses replicate through binary fission, it’s not a universal property. Many have more complex replication cycles involving host cell machinery.
• Contain equal proportions of protein, lipo polysaccharide and nucleic acids: This composition isn’t typical of viruses. Lipo polysaccharides are primarily associated with Gram-negative bacteria, and viruses generally have varying ratios of protein and nucleic acid, lacking LPS altogether.
• Contain DNA but no RNA: Although there are DNA viruses, many viruses exist solely with RNA as their genetic material. So, excluding RNA entirely wouldn’t be a general property.

Answer: Candidiasis

Candidiasis, specifically caused by Candida species (usually Candida albicans), is one of the most common opportunistic infections in individuals with AIDS. The weakened immune system in AIDS patients makes them susceptible to infections that would typically be controlled by a healthy immune system.

The other options are incorrect:

• Cryptococcosis: While cryptococcosis is a common opportunistic infection in AIDS, candidiasis is generally considered more prevalent.
• Tuberculosis: Tuberculosis is a common opportunistic infection in people with AIDS, but candidiasis is often more frequent and can affect various mucosal surfaces.
• Aspergillosis: Aspergillosis is another opportunistic infection seen in individuals with compromised immune systems, but it is less common than candidiasis in AIDS patients. Candidiasis tends to affect a broader range of individuals with AIDS.

Answer: Blood agar

Blood agar is a solid culture medium primarily used for growing bacteria. Viruses, however, require living host cells to replicate and cannot be cultured on non-living media like blood agar.

The other options are incorrect:

• Chick embryo: Avian embryos can be used for culturing certain viruses, particularly those that infect birds. For example, influenza virus is commonly isolated and propagated in chick embryos.
• Guinea pigs: As mammals, guinea pigs possess living cells suitable for some virus types to replicate. This allows them to be used as living models for studying viral infections.
• Cell culture: This method employs isolated and maintained populations of living cells (e.g., animal, human) in a controlled environment. It is a widely used and effective technique for culturing and studying a wide range of viruses.

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Answer: 6 week

The typical incubation period for hepatitis B after exposure through blood transfusion is around 6 weeks, ranging from 2 to 8 weeks. This period represents the time between initial infection and the onset of symptoms.

The other options are incorrect:

• 1 week: This is too short for the hepatitis B virus to replicate and cause noticeable symptoms or changes in blood tests.
• 3 months: While some cases might take longer, 3 months is generally considered beyond the typical incubation period for hepatitis B after blood transfusion.
• 6 months: This is too long for the initial acute phase of hepatitis B. Most cases would have progressed to either chronic infection or recovery within 6 months.

Answer: The time lapse between the infection and detection of viral antibodies

The window period in HIV infection refers to the time frame between contracting the virus and the point when a test can reliably detect HIV antibodies in your blood. This period typically lasts 23 to 90 days, depending on the type of HIV test used. During this time, the body is still developing its immune response to the virus, and antibodies haven’t yet reached detectable levels.

The other options are incorrect:

• The time lapse between the infection and development of AIDS: While HIV infection can eventually lead to AIDS if left untreated, the development of AIDS itself can take years or even decades. The window period specifically focuses on the initial detection of the virus, not the progression to later stages of the disease.
• The time lapse between obtaining the sample and detection of virus in the lab: This refers to the processing time within the laboratory and wouldn’t be considered the “window period” as it relates to the biological processes within the individual’s body.
• None of the above: This option is incorrect as the time lapse between infection and antibody detection accurately defines the window period for HIV testing.

Answer: Helper T lymphocytes (CD4)

Human immunodeficiency virus (HIV) primarily infects and destroys helper T lymphocytes (CD4), a critical part of the immune system. These cells play a crucial role in coordinating and directing the immune response against infections and diseases. By damaging CD4 cells, HIV weakens the body’s ability to fight off other viruses, bacteria, and even fungi, making individuals more susceptible to opportunistic infections and cancers.

The other options are incorrect:

• Red blood cells: While HIV can interact with red blood cells indirectly, it doesn’t directly infect them.
• Fibroblasts: These are connective tissue cells responsible for wound healing and structural support. HIV doesn’t target them directly.
• Mast cells: These cells are involved in allergic reactions and inflammation. They are not primary targets of HIV infection.

Answer: Pneumocystis carinii pneumonia

While all the listed infections can occur in individuals with acquired immune deficiency syndrome (AIDS), Pneumocystis carinii pneumonia (PCP) holds the title of the classic opportunistic infection in AIDS. This is due to its historical significance and widespread prevalence among HIV-positive individuals, particularly during the early years of the AIDS epidemic.

The other options are incorrect:

• Apthous stomatitis: While common in people with HIV, it’s not specific to AIDS and isn’t considered a classic opportunistic infection.
• Tuberculosis: A major global health concern, but its frequency in AIDS patients varies depending on geographical location and access to healthcare.
• Herpetic gingivostomatitis: A recurrent infection caused by herpes simplex virus, affecting the gums and mouth. While more common in HIV-positive individuals, it’s not as prevalent as PCP and doesn’t hold the same historical significance.

Answer: Orthomyxo virus, which is a RNA virus

Influenza is caused by Orthomyxoviruses, which are RNA viruses. These viruses have a segmented RNA genome and are classified into types A, B, and C. Influenza viruses are well-known for their ability to undergo frequent genetic changes, leading to the need for regular updates of flu vaccines.

The other options are incorrect:

• Paramyxo virus, which is a DNA virus: Paramyxoviruses are a different family of viruses that contain RNA, not DNA. They cause other diseases like measles, mumps, and RSV.
• Orthomyxo virus, which is a DNA virus: This option incorrectly states that Orthomyxoviruses are DNA viruses when they are actually RNA viruses.

Answer: Retro

The Human Immunodeficiency Virus (HIV) belongs to the genus Lentivirus, which is part of the larger family Retroviridae. Therefore, HIV is classified as a Retrovirus.

The other options are incorrect:

• Rheo: These are single-stranded RNA viruses that mainly cause mild respiratory and gastrointestinal infections in humans.
• Rhabdo: These are single-stranded RNA viruses that cause various diseases, including rabies and Ebola virus disease.
• Flavi: These are single-stranded RNA viruses that cause diseases like Dengue fever, West Nile virus, and Yellow fever.

Answer: Pox virus

Poxviruses are unique in their ability to induce the formation of both intracytoplasmic and intranuclear inclusion bodies within infected cells. These inclusions are aggregates of viral proteins and components, and their presence is a hallmark of poxvirus infection.

The other options are incorrect:

• Measles virus: While measles virus can cause intracellular inclusions, it doesn’t typically induce intranuclear inclusions.
• Hepatitis B virus: Hepatitis B virus can cause intracellular inclusions, but not intranuclear ones.
• HIV: HIV does not typically induce any type of inclusion bodies.

Answer: Rabies

Rabies is the only infection on this list for which post-exposure prophylaxis (PEP) in the form of immunization is crucial and effective even after infection has begun. This is because rabies has a long incubation period and once symptoms appear, it’s almost invariably fatal.

The other options are incorrect:

• Poliomyelitis: While a vaccine exists for polio, it’s given as a routine immunization to prevent infection before exposure. There is no effective post-exposure treatment for polio.
• Influenza: Influenza vaccines are also given before the flu season to prevent infection. There is no specific post-exposure treatment for influenza, though supportive care and antiviral medications can help manage symptoms.
• Herpes: There is no specific cure or post-exposure prophylaxis for herpes infections. Antiviral medications can help manage outbreaks and lessen symptoms, but they don’t eradicate the virus from the body.

Answer: 7-14 days

The incubation period for herpes zoster (shingles) is typically 7-14 days. This is the time between exposure to the varicella-zoster virus (VZV), which causes both chickenpox and shingles, and the onset of symptoms. After an initial infection with VZV (chickenpox), the virus can remain dormant in nerve cells and reactivate later in life, causing herpes zoster.

The other options are incorrect:

• 1 month: This option does not accurately represent the typical incubation period for herpes zoster. The correct range is 7-14 days.
• 1-2 years: This is not an accurate representation of the incubation period for herpes zoster. The correct range is shorter, occurring within 7-14 days.
• 3-6 months: This option does not reflect the usual incubation period for herpes zoster. The correct range is 7-14 days.

Answer: Composed largely proteins without any nucleic acid

Prions are unique infectious agents that differ significantly from viruses. They are composed entirely of proteins, lacking any genetic material like RNA or DNA. This characteristic distinguishes them from all other known infectious agents, including viruses, which always possess some form of nucleic acid.

The other options are incorrect:

• Phase in which virus cannot be demonstrated in host cell: This describes a viral latency period, not a specific characteristic of prions.
• Viruses which are genetically deficient: While some viruses can be defective, they still rely on nucleic acid for replication and transmission.
• Viral components may be synthesized but maturation & assembling is defective: This describes a type of defective virus, not a defining feature of prions.

Answer: Japanese encephalitis

Pigs are important reservoirs for the Japanese encephalitis virus, which mainly affects humans and horses. When infected mosquitoes bite them, they acquire the virus and potentially transmit it to humans through further bites. This makes pigs crucial in the transmission cycle of JE, despite not typically exhibiting severe symptoms themselves.

The other options are incorrect:

• Kuru: This rare prion disease primarily affected the Fore people of Papua New Guinea through ritualistic cannibalism, with pigs not playing a role in its transmission.
• Yellow fever: The primary reservoir for yellow fever is the Aedes aegypti mosquito, with monkeys serving as the main zoonotic hosts. Pigs are not involved in its transmission cycle.
• Rabies: While pigs can contract rabies and potentially transmit it to humans, their role in the overall transmission cycle is less significant compared to other reservoirs like dogs and wild animals.

Answer: Acquires its envelope from nuclear membrane

Herpesviruses are unique among enveloped viruses in that they acquire their envelope by budding through the inner nuclear membrane. This allows them to exit the nucleus without disrupting it and gain access to the cytoplasm where they can further mature and potentially spread to other cells.

The other options are incorrect:

• Acquires its envelope from the nucleolar membrane: The nucleolus is a specialized structure within the nucleus, not a separate membrane system. Viruses don’t acquire their envelope from the nucleolus.
• Acquires its envelope from the cytoplasmic membrane: While some viruses do bud through the plasma membrane (cytoplasmic membrane), herpesviruses specifically utilize the inner nuclear membrane for envelopment.

Answer: Protein coat

The presence of a protein coat (capsid or envelope) in viruses makes protective vaccines a possibility. Vaccines are typically developed to target specific viral proteins, such as those found in the capsid or envelope, to stimulate an immune response. This immune response produces antibodies that can recognize and neutralize the virus upon future exposure.

The other options are incorrect:

• Enzymes: While some viruses possess enzymes for specific functions, these internal components aren’t directly involved in immune recognition or vaccine development.
• Polysaccharide: Some viruses may have a polysaccharide component in their envelope, but the primary target for vaccine development is usually the protein capsid due to its immunogenicity and specificity.
• Lipids: Similar to enzymes, lipids are usually internal components of the viral envelope and don’t directly contribute to triggering the immune response necessary for vaccine development.

Answer: Nucleoproteins

Viruses primarily consist of genetic material (DNA or RNA) surrounded by a protein coat called the capsid. This combination of nucleic acid (nucleotides) and protein (scleroprotein) forms a complex called a nucleoprotein. When certain viruses crystallize, these nucleoproteins are the main component of the crystals.

The other options are incorrect:

• Nucleotides: These are the building blocks of nucleic acids (DNA and RNA), but they wouldn’t form the complete viral structure needed for crystallization.
• Phospholipids: These are components of some viral envelopes, but not the core nucleoprotein structure involved in crystallization.
• Scleroproteins: While these are a type of protein, they encompass a broad category and not all types are found in viruses. Specifically, the capsid proteins of viruses are nucleoproteins, which combine both scleroprotein and nucleotide elements.

Answer: All of the above

The HIV virus is relatively fragile and can be destroyed outside the body (in vitro) by all of these

• Boiling: Heating HIV-contaminated liquids or objects to boiling point (100°C) for at least 1 minute effectively denatures the viral proteins and nucleic acid, rendering them non-infectious.
• Ethanol: Alcohol disrupts the viral envelope and can inactivate HIV within minutes depending on the concentration and contact time. Ethanol-based hand sanitizers typically contain sufficient alcohol to be effective against HIV.
• Cidex: A glutaraldehyde-based disinfectant, Cidex kills HIV effectively due to its ability to cross-link proteins and damage viral structures.

Answer: Gastrointestinal tract

The primary portal of entry for the poliovirus is the gastrointestinal tract. After ingesting contaminated food or water, the virus infects the lining of the intestine. It then replicates within the gut and can subsequently enter the bloodstream, potentially reaching the nervous system and causing paralysis in severe cases.

The other options are incorrect:

• Nasal mucosa: While respiratory transmission of polio is possible, it’s much less common compared to the fecal-oral route. The virus can potentially enter through the nose and throat, but the gastrointestinal tract remains the primary gateway.
• Lung: Poliovirus doesn’t typically gain entry through the lungs. Although inhalation of aerosolized particles is theoretically possible, it’s not a major route of infection.
• Skin: The skin rarely acts as a portal of entry for poliovirus as it offers a strong physical barrier. Intact skin generally prevents viral penetration unless there are abrasions or open wounds.

Answer: High infectivity

The presence of Hepatitis B e antigen (HBeAg) in the blood of individuals with hepatitis B indicates a high level of viral replication and, consequently, high infectivity. HBeAg is a protein made by the hepatitis B virus, and its presence suggests active viral production and ongoing potential for transmission.

The other options are incorrect:

• Simple carriers: While someone with HBeAg can be considered a carrier, the presence of this antigen signifies active viral replication and high infectivity, unlike an inactive carrier state.
• Late convalescence: This refers to the recovery phase after an acute infection, where HBeAg is typically absent.
• Carrier status: Carrier status encompasses both HBeAg positive and negative individuals who harbor the hepatitis B virus, but only those with HBeAg positivity are highly infectious.

Answer: Lymphoma

While the other listed cancers can be associated with viral etiologies, Lymphoma generally does not have a confirmed viral cause. While Epstein-Barr virus (EBV) has been linked to certain types of lymphoma, like Burkitt’s lymphoma and Hodgkin lymphoma, it’s not considered the primary cause in most cases. Other factors like genetic predisposition and environmental exposures play a more significant role in lymphoma development.

The other options are incorrect:

• Carcinoma Cervix: Human Papillomavirus (HPV) infection is a major risk factor for cervical cancer.
• Hepatoma: Hepatitis B virus (HBV) and Hepatitis C virus (HCV) can contribute to the development of liver cancer (hepatocellular carcinoma).
• Nasopharyngeal carcinoma: Epstein-Barr virus (EBV) has been implicated in the development of some cases of nasopharyngeal carcinoma.

Answer: Extracellular infectious virus particle

A virion is defined as an extracellular, infectious virus particle. This means it’s a complete and assembled viral particle capable of causing infection in a host cell. It possesses all the necessary components, including viral genetic material (DNA or RNA) surrounded by a protective protein coat (capsid), to initiate infection and replicate within the host.

The other options are incorrect:

• Smallest virus: While virions may be incredibly small, the title of “smallest virus” can vary depending on specific measurements and classifications. Other factors like genome size and structure also contribute to virus size comparisons.
• A smallest particle similar to virus: This option is too vague and doesn’t accurately capture the specific characteristics and function of a virion. Not all small particles are viruses or possess infectious ability.

Answer: Viral interference

The phenomena where one virus particle prevents the multiplication of a second virus is known as viral interference. This interference can occur due to various mechanisms, such as competition for host cell resources, induction of host antiviral responses, or interference with the replication process of the second virus.

The other options are incorrect:

• Mutation: This refers to changes in the genetic material of an organism, which doesn’t directly explain how one virus can prevent another from multiplying.
• Supervision: This term isn’t used in a viral context and doesn’t accurately describe the interaction between different viruses.
• Permutation: This refers to the arrangement of items in a specific order, also not relevant to the phenomenon of viral interference.

Answer: Reo virus

The only virus known to have a double-stranded RNA genome is the Reovirus. Reoviruses belong to the Reoviridae family and are named for “respiratory enteric orphan” viruses. They possess a segmented double-stranded RNA genome, which is a distinguishing feature among viruses.

The other options are incorrect:

• Bunya virus: Bunyaviruses have a single-stranded RNA genome and do not possess a double-stranded RNA genome.
• Calci virus: There is no widely recognized virus family called “Calci virus.” The term may be a typo or misinterpretation. It does not represent a known virus family.
• Rhabdo virus: Rhabdoviruses have a single-stranded RNA genome. They do not have a double-stranded RNA genome like Reoviruses.